Rest assured you have not lost your milk. Your baby and you have worked out a schedule and your body has adjusted to make exactly what he takes. If you need to increase your yeild at the pump I suggest trying to pump one side while your son feeds on the other. But remember, no pump is as effective as a baby so don't judge your supply by what you see in the bottle.

Also assuming your baby is exclusively breastfed (no supplements), you can judge his milk intake by his wet and poopy diapers. At his age, 6-8 wet diapers and 2-4 poops the size of a quarter are sufficient. Poops should be yellow and seedy.

It could be the baby blues, but I think it's probably that you need to actually breastfeed rather than pump. I know that when I pump rather than breastfeed the yield is much lower. Try pumping while looking at him to see if that helps stimulate you. Or pump on one breast while breastfeeding the other.

Do be aware that sometimes the rush of milk in the first weeks can slow down once the baby settles into a regular nursing pattern. Also, the amount you pump isn't necessarily a good indicator of how much you are producing. I had plenty of milk for my daughter, but could never manage to pump out more than about an ounce. Are you nursing your baby on cue? Nursing on cue, and for as long as the baby wants to is the best way to ensure a stable milk supply.